Refining Uranium by the PUREX Process

PUREX is the major chemical technique for recovering uranium from spent nuclear fuel. Based on the highly-selective extraction of uranyl nitrate from aqueous solution by tributyl phosphate  (TBP) in a nonpolar organic solvent, the technique is straightforward for home chemists to exploit in order to refine their personal uranium stockpiles.  The photo illustrates the supplies used in the following procedure: nitric acid, tri-n-butyl phosphate (from QualityBiological.com), Kleen-Strip 1-K kerosene (Home Depot), and 4.8 g of homemade uranyl oxide.

Caution: the PUREX procedure involves intimately contacting nitric acid with highly-flammable organic material!  Work with small quantities.  Concentrated acid will form explosive oils, so always dilute it to 6M or less.  This discussion presupposes essential safety understanding of the chemicals and techniques involved.

New Crusher for Uranium Processing

Time to kick it up a notch in the uranium kitchen, since I got tired of crushing ore solely by hand with a hammer.  The new equipment to turn big rocks into very small rocks consists of a three-inch jaw crusher made by Al Yates, coupled to a 3.75-horsepower Briggs & Stratton Model #094202 gas engine.  To match the engine’s 3600 RPM at full throttle down to a safe speed at the crusher cam (and store some rotational energy for particularly resistant rocks), a 1.75″ pulley is used on the engine shaft and a heavy 11.75″ cast-iron pulley on the crusher shaft (both from McMaster-Carr).  The belt is a standard A50 size.  The whole deal is mounted on a wooden base.

This crusher can produce about 15 kg (a two-gallon pail) per hour of fine rock flour from 1-3″ Utah uranium ore.  It would take many tedious days to accomplish this with a hammer, seives, and a ball mill.  Now the slow step in my artisanal mining and processing scheme is acid leaching, and the attendant gravity filtration of sediment in the leachate.

Coming up soon…a look at the PUREX process—solvent extraction of uranyl nitrate into an organic phase.

RF Ion Source

I have been working on an ion source to support my next fusor and other small accelerator projects.  Criteria for this source were that it had to be easy and inexpensive to fabricate myself with common components from reliable sources.  My goals were to obtain high beam current and long service lifetime.  I settled on an RF ion source  concept with specific influences from Kiss and Koltay (1977).  Tests of the prototype indicate stable sub-milliampere currents of deuterium ions over hours of operation.  Cost (excluding RF and vacuum equipment): about $250.

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RF ion sources function by extracting ions from radiofrequency electrodeless discharges.  These sources can deliver high-purity beams of atomic H+ ions.  The vessel supporting such a discharge can be as simple as a glass test tube surrounded by an inductive coupling to the RF supply, as my design at left illustrates.  The discharge is “enhanced” with the field from a strong magnet.  Some builders attempt to exploit specific enhancement effects, e.g. electron cyclotron resonance or helicon phenomena.  My goal with the magnet is just to promote generic electron trapping / heating, possibly by the above-mentioned modes if conditions are appropriate.  Components, with suppliers’ names and stock numbers, are provided in the drawing.

Construction techniques involve drilling, lathe turning, silver brazing, and soft silver soldering.  Photos at left show components of the source  (most prominent are the extraction electrodes) during assembly on a ConFlat cube for testing.

Extraction of ions is accomplished by a strong DC electric field imposed between the negatively-biased “nozzle” on the 5/16″ tube and the grounded septum on the 1/2″ tube.   I use up to -5 kV for extraction of ions.  The extraction nozzle also throttles neutral gas flow from the discharge region into the vacuum chamber.

RF power is supplied by an FAA-surplus AM-6155 power amplifier operating at 200 MHz.  These amplifiers are a common hamfest bargain.  Circuit details and modifications for the amateur radio hobby are easy to find online.  To date I have not produced more than ~60W with this amplifier, driving it with signals below 1W.  Beam current depends very strongly on RF power, and I plan to upgrade the driver for the AM-6155 to produce more.  The top photo shows this amplifier producing power (lighting a mercury-vapor discharge), and the bottom photo shows the tube compartment of the amplifier modified for shunt feed of plate current.

Inductive coupling of the 200-MHz power to the discharge plasma is effected with a single loop of heavy conductor that forms part of a resonant “L-match” circuit, providing an easy interface to 50-Ω cable.  This is illustrated schematically at left.  The right photo shows the ion source ready for testing, with the RF coupling loop visible along with other components including gas for the discharge (deuterium lecture bottle).

Photos from operation.  The top photo shows the RF deuterium discharge in a standard 19-mm (3/4″) Pyrex test tube, and below it a beam of extracted ions impinging on a graphite Faraday cup target.  RF power is about 50W, extraction voltage -3 kV, and target at -10 kV.  Background pressure has been raised into the millitorr range to enhance beam visibility.  Extracted current is 0.25 milliampere.  Bottom photo shows the exit aperture clearly, with deuteron beam passing through a ring electrode at -10 kV.  Here the extraction voltage was -5 kV.  It is not possible to accurately measure the beam current in this arrangement, but it is probably on the order of 0.5 mA.  Not surprisingly, a few neutrons from ²H(d,n) fusion reactions can be detected with higher potentials on the ring cathode.

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More information about this ion source

• Original description
• Discussion of AM-6155 RF supply
• A bit of operational data
• More recent modifications
• Improvement to the discharge bottle involving a little glassblowing

Experiments with a Tiny Radioisotope Neutron Source

By placing beryllium in intimate contact with an alpha-emitting radioisotope, neutrons are produced. At home, one can approach this well-known reaction by lining up the sealed americium sources from a quantity of old-fashioned ionization smoke detectors on a sheet of beryllium metal. The neutron yield is easily detected; see this link for more information. My own toy AmBe neutron source currently produces an estimated 1000 neutrons per second. That makes it more than three orders of magnitude weaker than my Farnsworth Fusor. But are there enough neutrons to perform some detectable nuclear reactions? As it turns out…yes.

Neutrons give rise to prompt gamma rays when they are captured by many nuclei. The following experiments involve the detection of high-energy (> 4.4 MeV) gamma signatures from neutron capture in chlorine, iron, and titanium, in the form of inexpensive and readily-available compounds mixed with water and placed near the 1000 n / s AmBe source. A gamma ray spectrum is collected with a very efficient scintillation detector (2×2″ BGO) over a period of hours.

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Setup

For the chlorine experiment, a 40 lb. bag of rock salt was purchased at Lowe’s for about $4. A two-gallon pail was filled to the brim with salt, followed by successive additions of water and more salt to obtain the highest chlorine density possible. A piece of PVC pipe, capped on the bottom, enters the salt pail from the top. The neutron source fits down in this pipe so that it is nearly surrounded on all sides by salt. The lead-shielded BGO scintillator views the side of the pail at the level of the source.

The iron experiment is similar, except the medium in use is 10 lb. of ferrous oxide (FeO) purchased at New Mexico Clay here in Albuquerque. The oxide is divided among two PETE jars and water is added to wet the oxide, drive out air, and fill the jars. The neutron source is taped behind one of the jars and the assemblage is surrounded by UHMW-PE bricks to act as a neutron moderator / reflector.

Titanium was obtained in the form of titanium dioxide powder from New Mexico Clay. Enough dioxide (~8 lb) was loaded into a large cylindrical Rubbermaid food-storage container to fill the sonofabitch. Water was added to displace air and top off, and as before, PE bricks were arranged around the outside. In this instance the neutron source sits in an acrylic tube penetrating the TiO₂ from the top.

Results follow below…

Uranium Chemistry

Uranium and its pure compounds are just not readily available to the amateur scientist, element collector, or student in 2008. So what is one to do? Make these materials oneself, of course. (At left is a quantity of home-baked yellowcake.)

This is the inaugural post in what will become a short series, detailing how uranium and various pure compounds can be refined from the brute earth to serve personal needs. There are differences between what is done in industrial mining / milling operations and what can be realistically accomplished in a typical American domicile. There are also differences in the raw materials that could be obtained back in the good old days when our favorite applied inorganic chemistry texts were written (“Borrow a gallon of fuming nitric acid and some glycerin from your science-teacher…”), versus what can be obtained in the paranoid, restrictive world of today. Thus, my approach to uranium chemistry emphasizes practical techniques and materials that are available to today’s home-dweller. The foregoing discussion assumes a decent background in chemistry and mature attention to safety.

Uranium compounds that can be easily prepared at home are shown in this photo. In vials, left to right: uranyl oxide (UO₃); uranyl peroxide (UO₄·nH₂O); triuranium octoxide, U₃O₈; sodium diuranate (Na₂U₂O₇·6H₂O); uranium tetrafluoride (UF₄·2.5H₂O); “sodium peruranate” in solution; uranyl chloride (UO₂Cl₂) in solution. In front is an electroplated layer of uranium dioxide (UO₂). Click “more” below for content (I will upload it as time permits).